1. Field of the Invention
The present invention relates to the treatment of wastewater effluent from a commercial car wash.
2. Background and Discussion of the Prior Art
Commercial car wash operations desire to discharge their effluent to subsurface aquifers, or to the surface, or reuse the treated water as feedwater. Present day state and local environmental restrictions place severe limitations on the organic matter, solids, volatile organic compounds (VOC) and heavy metals permitted to be discharged to the environment. Car wash businesses desire an effluent treatment system which meets these present day rigorous environmental standards and yet permits essentially continuous operation with minimal downtime, and in which maintenance is achieved in a practical manner with minimal cost by persons of limited technical skill.
Environmental agencies in various locales throughout the country have recently set and enforced rigorous maximum discharge criteria standards for commercial wastewater. Car washes in certain locales face particularly stringent wastewater effluent permissible maximums. For example, the New York State Department of Environmental Conservation (NYSDEC) Regulation, Title 6, Chap. X, Section 703.6, eff Jan. 9, 1994 provides such stringent effluent standards, particularly for heavy metals found in car wash effluent, as well as for oil and grease, pH as follows:
TABLE 1 ______________________________________ Maximum Allowable Concentration Substance (micrograms/liter, ug/l) ______________________________________ Barium 2,000 Cadmium 20 Chromium (hexavalent) 100 Copper 1,000 Foaming agents.sup.1 1,000 Iron.sup.2 600 Lead 50 Manganese 600 Nickel 2,000 Oil and Grease 15,000 pH See Note 3 Zinc 5,000 ______________________________________ Notes. 1. Foaming agents determined as methylene blue active substances (MBAS) o other tests as specified by the commissioner. 2. Combined concentration of iron and manganese shall not exceed 1000 ug/L. 3. pH shall not be lower than 6.5 or the pH of the natural groundwater, whichever is lower, nor shall be greater than 8.5 or the pH of the natura groundwater, whichever is greater.
Commercial car washes peculiarly face gasoline residues which are found in the effluent and must also be removed. These gasoline residues particularly include the volatile organic compounds (VOC): toluene, xylene (per monomer), ethyl benzene and benzene. Thus, car wash operations were required, pursuant to NYSDEC Regulation, Title 6, Chap. X, Sections 703.6, 702.16(c)(1) and 702.15, to reduce such volatile organics in the discharge effluent to the following limits:
TABLE 2 ______________________________________ Maximum Allowable Concentration Volatile Organic (VOC) (parts per billion, ppb) ______________________________________ Toluene 5 Xylene (per monomer) 5 Ethylbenzene 5 Benzene 0.7 ______________________________________
The effluent from car wash operations varies substantially, particularly on whether and to what degree there is recycle. A typical car wash discharge however has the following typical concentrations and range of concentrations:
TABLE 3 ______________________________________ Concentration Ranges (parts per million, Substance ppm) ______________________________________ MBAS 3-40 ppm TSS 50-250 ppm Oil and Grease 10-200 ppm pH 7-9.5 Barium 0.15-0.30 ppm Lead 0.02-0.30 ppm Chromium 0.05-0.30 ppm Cadmium 0.02-0.15 ppm Manganese 0.10-2.0 ppm Copper 0.10-0.40 ppm Zinc 0.30-3.0 ppm Iron 0.50-20.0 ppm Volatile Organics (VOC) 300-600 ppm total ______________________________________
"MBAS" refers to "methylene blue active substances" and "TSS" refers to "total suspended solids", as determined by conventional testing methods well-known to those skilled in the art. "FOG" refers to "fats, oils and greases". "Oil and grease" is understood to mean essentially "FOG".
The present day car wash operations were thus faced with the daunting task of reducing not only the oil and grease as was the earlier concerns, but also substantially reducing heavy metal concentrations, VOCs and MBAS.
Typical early, and now apparently impractical, prior art approaches were to use generalized wastewater treatments, deemed suitable for a wide range of commercial or industrial operations. One such early attempt for both a car wash and laundry treatment is disclosed in U.S. Pat. No. 4,104,164, granted Aug. 1, 1978, to Chelton. Chelton disclosed a generalized approach to wastewater treatment, which provided for a first stage treatment by a weir or gravity filtration of the effluent followed in seriatim by centrifugation, activated carbon adsorptive filtration, bag filtration and particulate filtration. While Chelton describes the treatment as being suitable for both car wash and laundries, the present day discharge standards particularly as to certain heavy metals appear to render the Chelton and like laundry treatment systems unsuitable. By way of example, due to the types and concentrations of heavy metal contaminants in solution and required to be removed in present car wash operations, the Chelton primary reliance on centrifugation and filtration would be misplaced. Another prior art method use for both laundry and car wash wastewater treatment is Arnaud, U.S. Pat. No. 5,647,977. Arnaud discloses mixing/flocculating as a treatment step. The laundry/car wash prior art methods were not generally directed to the removal of heavy metals in diverse concentrations.
The present day car wash art thus desired a method and apparatus for treating its wastewater effluent to remove substantial heavy metals as well as FOGs in an essentially continuous operation, in a non-toxic, moderate pH environment, and with minimal maintenance and downtime, and yet importantly meet the present day stringent environmental discharge standards. The present invention provides that desired result.